Island Arc最新文献

The mechanism of Caledonian orogeny in South China is still controversial. The main argument focuses on the issue that whether there existed oceanic subduction. To answer this question, the complex Puyang pluton in the central part of Wuyi orogenic belt was selected for zircon U–Pb dating, in-situ Lu–Hf isotopic analysis and geochemical testing. The Puyang pluton is mainly composed of granodiorite and diorite. The results of geochronology indicate that the granodiorite and diorite emplaced at 450 ± 3.9 Ma and 443 ± 4.0 Ma. Their emplacement time were well corresponding to the subduction stage of the Yunkai orogeny in the southwestern part of Cathaysia block during the Early Paleozoic (460–440 Ma). The Puyang adakite-like granodiorite shows enrichments in Sr, but depletions in Y and Yb contents, high in Na₂O, K₂O and Al₂O₃, with ε_Hf(t) values range from −10.5 to −7.4 (mean of −9.0) and two-stage Hf model ages range from 1.91 to 2.10 Ga. These characteristics indicate that the magmas were generated by partial melting of subducted oceanic crust mixed with melts from the above wedgy mantle peridotite. The Puyang high-Mg diorite shows enrichments in Sr and Ba, depletions in Rb, Y and Yb contents, and strongly high in MgO and Al₂O₃ contents, with ε_Hf(t) values of −2.9 to 0 (mean of −1.4) and two-stage Hf model ages of 1.43 to 1.61 Ga. These indicate that the magmas were mainly generated by partial melting of the wedgy mantle peridotite, mixed by adakitic melts from subducted oceanic slab. Comprehensive analysis shows that Puyang adakite-like granodiorite and high-Mg diorite were formed in fore-arc setting, where the mantle and crustal magmas mixed during the oceanic subduction initiation period. By extension, this study offered important evidences to support the point that the Caledonian orogeny in South China was related to oceanic subduction which initiated prior to ~450 Ma.

The NE Jiangxi ophiolitic mélange belt is the key area for understanding the evolution of the Paleo-South China Ocean and the assembly of the Yangtze and Cathaysia blocks. The age of the deformed matrix is closer to the tectonic emplacement time of the ophiolitic mélange than that of the blocks. However, the rock types, ages and structural deformation of the matrix in the NE Jiangxi ophiolitic mélange belt lack comprehensive understanding. Based on the zircon U–Pb geochronology, Hf isotope and trace element analyses of the deformed matrix in the NE Jiangxi ophiolitic mélange belt, we report the ages of meta-rhyolite and tuffaceous phyllite to be 800–760 Ma, and the maximum depositional age of the clastic matrix is ~760 Ma. The youngest deformed matrix ages of 800–760 Ma constrain the tectonic emplacement age of the NE Jiangxi ophiolitic mélange belt to the late Qingbaikou period after 800–760 Ma and before the deposition of the Xiuning Formation (765–732 Ma). Zircon ages, trace element and Hf isotope compositions indicate that the 800–760 Ma matrix was formed in a back-arc basin environment with obvious addition of 1000–800 Ma arc materials and recycled Paleoproterozoic crustal materials. The detrital material source areas were the 800–760 Ma arc and earlier accretionary wedge as juvenile crust. The multi-stage arc magmatism, metamorphism and deformation in the NE Jiangxi ophiolitic mélange belt suggest that multi-stage subduction of the Paleo-South China Ocean and Neoproterozoic accretionary orogeny occurred during 1–0.76 Ga at the southeast margin of the Yangtze Block. Combined with the regional geological data, the Neoproterozoic back-arc basin or the foreland basin around the Yangtze Block closed after ~760 Ma. The collision and amalgamation of the Yangtze and Cathaysia blocks resulted in the final closure of the Paleo-South China Ocean, which have occurred in the early Paleozoic.

Yamaguchi, T., Nanayama, F., Nakanishi, T., Tsuji, T., Ikeda, M., Kondo, Y., Miwa, M., & Hamada, Y. (2022). Middle Holocene relative sea-level changes and vertical tectonic crustal movements on Shikoku Island near the Nankai Trough, Japan. Island Arc, 31(1), e12452. https://doi.org/10.1111/iar.12452

On page 9, third paragraph, the Dryad Digital Repository link (https://datadryad.org/stash/share/Caof8eH1lrqg2vUUvuH20N71TqbLAOHBt4g5ydr8W2g) is outdated and inaccessible. The link has been updated and can be accessed on https://datadryad.org/stash/dataset/doi:10.5061%2Fdryad.pc866t1kk.

We apologize for this error.

The Lohit Plutonic Complex (LPC) of Arunachal Trans-Himalaya represents the northeast extension of Trans-Himalayan magmatic arc system located in the north of Indus Tsangpo Suture Zone (ITSZ). Field relation, magnetic susceptibility (MS), and phase petrology on the granitoids of LPC was conducted in order to assess the granite series (magnetite, oxidized vs. ilmenite, reduced types), and physico-chemical conditions of the LPC granitoid magmas. The studied granitoids are well-exposed in the Dibang and Lohit valleys, and their MS values indicate a bi-modal patterns corresponding to ilmenite (reduced) series (71%) and magnetite (oxidized) series (29%) granites. The variation of MS in the LPC granitoids is related to the alteration of ferromagnetic minerals, and later tectonic and deformational processes that acted upon them. The amphiboles from the LPC granitoids are calcic (Ca_B >1.5, Si = 6.30–7.06 apfu) and exhibit tschermak substitutions typical to their evolution in a calc alkaline, metaluminous (I-type) felsic magmas. Al-in-hornblende rims estimate the emplacement of quartz diorite and granodiorite magmas at shallow (~5 km) and mid (~16 km) crustal depths. Geothermometric results point to a regime of magmatic crystallization (940–837°C for quartz diorite; 882–829°C for granodiorite) sufficiently above the solidus of respective melts. Biotites from LPC granitoids are primary to re-equilibrated, and transitional between magnesio- and ferri-biotites. Quartz diorite and granodiorite biotites evolved under oxidizing magmas (log ƒO₂⁻¹⁴ to log ƒO₂⁻¹³) in a temperature range of ~750–950°C, typical to their formation in a calc alkaline magma of subduction zone environment. However, the biotites from leucogranite appear to have evolved under a mildly reducing magma environment, most likely attained in a collisional setting. The obtained results suggest that the oxidized nature of calc alkaline, subduction-related magmatic arc rocks of the LPC is largely modified and reduced by post-magmatic, and later tectonothermal and deformational events that operated during Himalayan and Trans-Himalayan orogenesis.

The Ilgın geothermal field that is the oldest and most important spa of the Konya Region is located in Central Turkey. The Ilgın geothermal field has five geothermal wells and three hot water springs with flow rates of 40–130 L/s, temperatures 26–42°C and depths of 120–300 m. In the present study, detailed hydrogeochemical investigations are carried out to understand the geothermal energy potential of the thermal waters. The chemical properties of the cold and hot waters collected from the field were determined and the classification and usage possibilities of the waters were investigated. The thermal well water samples have the same Cl, B and Li concentrations in rainy and dry seasons, but those of the other samples are variable in rainy and dry seasons. This suggests the surface water mixtures were constant in hot water wells or that the precipitation times were long. In the Li-Rb-Cs diagram, the Li/Cs ratios of hot waters are 6.53–8.61 in the rainy period and 6.28–8.47 in the dry period, indicating that they are derived from acidic rocks. According to their isotopic composition, it can be said that the waters are of meteoric origin. According to the Langelier, the Ryznar and the Puckorius Saturation Indexes, the waters can precipitate carbonate. The waters interacted with gypsum and anhydrite zones based on the Halite Saturation Index, while the waters are associated with dolomite-rich rocks in terms of the Dolomite Saturation Index. Silica and cation geothermometers except Na-K applicated to the Ilgın geothermal waters yielded similar reservoir temperature estimates (e.g., 13–76°C for rainy period, 10–80°C for dry period). However, reservoir temperature from the other estimates (Na-K geothermometers, enthalpy-chloride diagram and enthalpy-silica mixture model) are higher than 103°C. Taken as whole, the temperature estimates exhibit little agreement between the different geothermometry calculations suggesting that the Ilgın geothermal waters represent immature waters, and water-rock equilibrium in the geothermal reservoir was not fully attained.

Tracking paleoenvironmental change and past event deposits is very important to evaluate the natural hazard spatially. This paper presents how the environment changes and implies the event deposit depending on the diatom assemblage change. To investigate paleoenvironmental change and identify the difference between tsunami and typhoon deposits, we analyze diatoms from the sediments in two coastal lakes in southern Japan where flood deposits have been linked to historical typhoon and tsunami events (Lakes Kawahara and Ryuo). The sediment cores extend from B.C.E. 500 to approximately C.E. 1000 and the downcore variation in diatom assemblages indicates a series of transitions from saline to fresher conditions in both Lake Kawahara and Lake Ryuo between approximately C.E. 500 and 1700. We observe an obvious deviation in diatom assemblages in event deposits previously identified to be either of tsunami or typhoon in origin. For the most prominent event deposit preserved in Lake Ryuo by the Hoei tsunami of C.E. 1707, the deposition of marine diatoms serves as evidence of marine flooding, while the subsequent deposition of soil and freshwater diatoms indicates the mobilization of terrigenous sediment during returning seaward flows. In contrast, the most prominent event deposit in Lake Kawahara is associated with freshwater flooding by the Kamikaze typhoon of C.E. 1281 and contains very low diatom abundances and a peak of freshwater taxa, followed by a peak in diatom counts potentially due to greater biological activity induced by a resultant influx of nutrients and re-oxygenation during the event.

To identify the origin of the Hida belt in central Japan, geochemistry and U–Pb age of zircons were analyzed for the extra-large granitoid boulders in the Lower Cretaceous fluvial conglomerate of the Jinzu Group. This study clarified that the boulders of granitoids have geochemistry of typical A-type granite, as characterized by high Nb + Y and high Ta + Yb values. U–Pb ages of igneous zircons from three individual granite boulders are concentrated at ca. 220 Ma (Late Triassic). As to Late Triassic A-type granites, there is no corresponding body previously recognized within Japan, whereas identical A-type granites occur in the eastern Songliao block on the immediate west of the Jiamusi block in NE China. The large size of boulders and the fluvial facies of the hosting conglomerate indicate their origin in the Hida belt per se, suggesting the cryptic and/or past occurrence of A-type granite, rather than in NE China. Together with the eastern Songliao block (China), Laoelin-Grodekov (LG) belt (Primorye, Russia), and Yamato Ridge (Japan Sea), the Hida belt forms a unique domain on the immediate west of GSC in Far East Asia, which is characterized commonly by the co-occurrence of Permo-Triassic and Jurassic granitoids, and probably with Late Triassic A-type granite. These confirm that Hida belt represents an allochthonous unit tectonically emplaced onto the rest of Japan, which is composed of the Phanerozoic subduction-related orogenic belt (Nipponides) developed along the Pacific side of Greater South China (GSC) since the Cambrian. For emphasizing a major geotectonic boundary of the Mesozoic granitoid provinces in Far East Asia, we propose the Yamato tectonic line between the easternmost Central Asian orogenic belt and GSC/Nipponides, which is traced for up to 3000 km from the Russia/China/North Korea border to SW Japan.